The present invention is relates to seals and particularly to static gaskets for various encapsulating covers and especially fuel cells.
Fuel cells are one of the leading alternate fuel powerplant candidates which, if commercialized, can dramatically reduce urban air pollution, decrease oil imports, reduce trade deficits and produce more jobs. Fuel cells are being developed for both portable and stationary electrical power generation.
A fuel cell is an electrochemical energy converter consisting of two electrodes which sandwich an electrolyte. In one form being developed for both portable and stationary applications, an ion-conducting polymer electrolyte membrane is disposed between two electrode layers to form a membrane electrode assembly (MEA). The MEA is typically porous and electrically conductive to promote the desired electrochemical reaction from two reactants. One reactant, oxygen or air, passes over one electrode and hydrogen, the other reactant, passes over the other electrode to produce electricity, water and heat.
An individual cell includes an MEA placed between a pair of separator plates. The separator plates are typically fluid impermeable and electrically conductive. Fluid flow passages or channels are formed on each plate surface adjacent to the electrode layer to facilitate access of the reactants to the electrodes and the removal of the products of the chemical reaction. In such fuel cells, resilient gaskets or seals are typically provided between the faces of the MEA and the perimeter of each separator plate to prevent leakage of the fluid reactant and product streams.
In U.S. Pat. No. 5,464,700, an elastomeric gasket is placed on either side of the ion conducting membrane and the two electrode layers are placed on the gasket to form a five layered gasketed MEA. The gaskets are difficult to assemble because they are flexible and they have a tendency to twist. This makes proper alignment of the five components time consuming and prone to misassembly. Thus., this gasket has not been widely adapted.
U.S. Pat. No. 6,080,503 discloses an integral seal with an adhesive bond that is formed between pairs of separator plates and the MEA. Alternatively, adjoining pairs of separator plates in the fuel cell stack are adhesively bonded together. Such an arrangement is easier to assemble and less prone to misalignment but does not facilitate the repair and/or removal of separator plates after the stack has been assembled. It has been found that it is difficult to disassemble the adhesively bonded stack without tearing the MEA or causing the separator plate, which may be brittle, to break.
Another solution using an integral seal that circumscribes the MEA is disclosed in U.S. Pat. No. 6,057,054. In this case, the sealing material is impregnated into the porous electrode layers near the sealing region. This seal has also been found to be difficult to make without damaging the MEA.
Thus there is a need for a reusable fuel cell stack which can prevent leakage of fluid reactants and product streams that can be easily assembled to the ion conducting polymer electrolyte membrane and the two electrode layers and the corresponding mating separator or flow field plates.